The series hybrid electric vehicle designates a vehicle configured to drive an electric generator by an internal combustion engine (engine), to supply electric power from the electric generator to a motor, and to drive drive-wheels by the motor, as disclosed in US 2007/0137908 A1, as an example. In a series hybrid electric vehicle, the engine is dedicated to generating electric energy; the mechanical energy generated by the engine is not directly transmitted to the drive-wheel, in contrast to a parallel hybrid electric vehicle, where some mechanical energy generated by an engine is directly transmitted to a drive-wheel.
One example of a hybrid electric vehicle is described by Japanese Unexamined Patent Application Publication No. 2005-204370.
This example discloses a hybrid electric vehicle configuration that uses a diode rectifier to reduce the loss of electric energy generated by the system by rectifying current generated by a motor-generator driven by the engine and then driving a motor connected to a vehicle driving system.
When an output current from the motor-generator is rectified by the diode rectifier as disclosed in this related reference, the loss of electric energy generated by the system can be reduced.
However, the inventor herein has recognized a disadvantage with the approach used in this related reference. Specifically, since a diode rectifier passes a direct current, a motor-generator will not work as a starter for an engine due to the unidirectional flow of the direct current. In one approach, to address this problem, an inverter may be placed between the diode rectifier and the motor to power the motor-generator during an engine start. However, this approach introduces another problem; specifically, a motor cannot be driven during an engine start when a driving motor is required.
Further, since a capacity requested for an inverter changes significantly depending on vehicle operating conditions, when the vehicle is operating under a certain condition where the inverter is operated with an output much smaller than a rated output, the inverter cannot be used efficiently due to a decreasing inverter loading rate.
Therefore, there is a need for providing a hybrid electric vehicle that can make effective use of an inverter to operate with higher efficiency.
One example embodiment of the present description is a hybrid electric vehicle comprising: a motor-generator driven by an engine to generate alternating current and serving as a starter driving the engine when the engine is started, a motor for driving the vehicle, a diode rectifier for rectifying alternating current generated by the motor-generator, an inverter connected to a feed circuit between the diode rectifier and the motor and converting direct current in the feed circuit into alternating current, a power supply connected to a line connecting the diode rectifier with the inverter, a first feed circuit for supplying current to a motor for driving the vehicle through the diode rectifier and the inverter in series, a second feed circuit to connect the motor-generator with the power supply while bypassing at least the diode rectifier and an alternating current converter provided in the second feed circuit.
This hybrid electric vehicle overcomes at least some of the disadvantages of the approach of the related reference described above.
In an example embodiment, the hybrid electric vehicle may further comprise a controller for controlling power distribution to a first feed circuit and a second feed circuit, wherein the controller includes: an operating condition determining module for determining an operating condition of the vehicle, wherein determining the operating condition includes determining a demand for cranking the engine using the motor-generator; and a cranking control module for supplying power from the power supply to the motor-generator via the second feed circuit when a cranking demand is detected.
In one example embodiment, the alternating current converter is a semiconductor switch.
In another example embodiment, the alternating current converter is a second inverter placed in parallel with the first feed circuit. And, the hybrid electric vehicle further comprises: a switch device to selectively switch between a motor power feeding mode where the power supply is connected to the motor via the second inverter and a starter power feeding mode where the power supply is connected to the motor-generator via the second inverter.
As a nonlimiting example, one or more relay switches or insulated gate bipolar transistors, etc., may be used as an element of the “switch device”.
In one example embodiment, the switch device may be a relay switch. In this example, a hybrid electric vehicle may further comprise a controller configured to switch the relay switch from one mode to another after turning off the second inverter, for example, when a switch is requested while the second inverter is in an on-state.
In another example embodiment, a hybrid electric vehicle may further comprise a feed line for an electric load, the feed line provided in a switch device, and an electric component, such as a 100V alternating current source and/or an air-conditioning unit for a vehicle cabin, as non-limiting examples, wherein the electric component is connected to the feed line such that the second inverter can feed to the electric component.
In another example embodiment, the cranking control module may be configured to control the inverter and the second feed circuit such that electric power generated by the power supply is supplied from the inverter to the motor-generator via the second feed circuit while driving current for the motor from the inverter is restricted, when it is determined that there is a cranking demand while the vehicle is stopped.
In another example embodiment, the cranking control module may be configured to control the inverter and the second feed circuit such that direct current from the power supply is converted to alternating current in the alternating current converter and the alternating current is provided to the motor-generator.
In another example embodiment, the motor-generator is a polyphase alternating current device, and the cranking control module is configured to control the inverter and the second feed circuit such that direct current from the power supply is converted to high frequency monophase alternating current in the inverter and, the monophase alternating current is converted to polyphase alternating current having the same phase number as the motor-generator, and the polyphase alternating current is provided to the motor-generator.
In another example embodiment, the hybrid electric vehicle may further comprise a switch between the inverter and the motor, wherein the cranking control module is configured to control the inverter, the second feed circuit and the switch such that the switch is shut off before current is fed from the power supply to the motor-generator, when there is a cranking demand while the vehicle is stopped.
In this way, at least some of the disadvantages of the related reference described above are overcome.